cmd/compile/internal/escape: mark blankLoc as transient

Discarded values never persist, so they can be transiently allocated
too.

Change-Id: I036ce0c1eea45e437142497bb7df3ecb44b56e52
Reviewed-on: https://go-review.googlesource.com/c/go/+/520256
Auto-Submit: Matthew Dempsky <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Cuong Manh Le <[email protected]>
Run-TryBot: Matthew Dempsky <[email protected]>

Author: mdempsky

src/cmd/compile/internal/escape/escape.go

@@ -130,6 +130,7 @@ func Batch(fns []*ir.Func, recursive bool) {
 
 	var b batch
 	b.heapLoc.escapes = true
+	b.blankLoc.transient = true
 
 	// Construct data-flow graph from syntax trees.
 	for _, fn := range fns {